By Zac Unger
17 December 2012
On January 24, 2004, in the frigid moonscape of an Arctic winter, wildlife biologist Steven Amstrup rode in a helicopter flying low over the ice. Using an infrared heat detector, he hoped to find polar bears in their dens. When the gun recorded a hit, Amstrup circled around for a closer look. What confronted him was something he had never seen in 34 years of research. The mouth of the den was open, and a smear of bright-red blood stretched away for more than 200 feet. At the end of a long drag trail in the ice lay the still-warm body of a female polar bear. The air temperature was 20 degrees below zero; this bear could not have been dead for more than 12 hours.
Polar bears do not have enemies. A male can weigh 1,500 pounds, with paws a foot wide and savage teeth. They are the unchallenged master predators in the harshest environment on Earth. A full-grown bear slaughtered in her den is far outside the ordinary.
Amstrup and his team returned by snowmobile. The dead female had multiple wounds to her neck and head, and the snow was stained by heavy arterial bleeding. Her skull had been pierced by a long tooth that slammed into her brain. Her hindquarter, belly, and mammaries were partially eaten.
Inside the den, Amstrup found two tiny cubs, each weighing less than five pounds. Both were dead, suffocated by the thick snow of the ruined cave. A single set of massive footprints led directly to the den. The footprints followed a typical hunting pattern—the stalker meandered around in a wide arc, then beelined for the spot where the mother and cubs were resting. There was only one explanation for this carnage: the bear and her cubs had been killed by another polar bear.
Cannibalism is not normal polar bear behavior. Seals are easier to catch and their meat has more calories per pound than bear meat. But over the course of that single season, Amstrup witnessed two additional instances of cannibalism. Having never seen anything like this, he was shocked to stumble across three separate incidents in one year. But as he spoke to colleagues, he found that cannibalism was becoming more common. In the Svalbard Archipelago, 450 miles north of Norway, three small cubs had been found dead inside their den. Although polar bears sometimes kill each other, these were the first recorded instances in which the killing took place at the supposedly safe haven of a den.
The past decade has been particularly difficult for polar bears. The summers of 2002, 2003, and 2004 saw a sharp increase in ice-free water. Between 1987 and 2003, scientists saw 12 polar bears swimming in open water, miles out from the edge of the pack ice. But in 2004 alone, scientists saw 10 bears swimming in open water, several as far as 110 miles offshore. Even more alarming, scientists found four polar-bear carcasses floating in the sea; they had apparently drowned while attempting to swim from one ice floe to the next. Never before had scientists seen even a single drowned bear. On land, the scientists found that half the bears were lean or emaciated. In western Hudson Bay, near the town of Churchill, Manitoba, a 2007 study told a grim tale: in less than 20 years, the local bear population had plummeted from 1,194 to 935, a decline of more than 20 percent. Around the Arctic, the pattern was consistent, and scientists were building the case that polar bears were the first in a long series of future calamities attributable to global warming.
Amstrup, who had written many of the papers detailing the bears’ precipitous decline, was beginning to understand the carnage; the polar bears were turning to cannibalism because they were starving to death.
Or at least that’s how it was reported. […]